1. Field of the Invention
The present invention relates generally to blast nozzles used to propel abrasive particles in a pressurized fluid such as air or water against a solid surface to remove adherent material, such as paint, scale, dirt, grease and the like therefrom. In particular, the present invention is directed to an improved blast nozzle holder which securely attaches the supply hose to the blast nozzle.
2. Description of the Prior Art
In order to clean a solid surface so that such surface can again be coated such as, for example, to preserve metal against deterioration, or simply to degrease a solid surface such as surfaces contacting food or building structures which contain food serving or food processing operations, it has become common practice to use an abrasive blasting technique wherein abrasive particles are propelled by a high pressure fluid against the solid surface in order to dislodge previously applied coatings, scale, dirt, grease or other contaminants. Various abrasive blasting techniques have been utilized to remove the coatings, grease and the like from solid surfaces. Thus, blasting techniques comprising dry blasting which involves directing the abrasive particles to a surface by means of pressurized air typically ranging from 30 to 150 psi, wet blasting in which the abrasive blast media is directed to the surface by a highly pressurized stream of water typically 3,000 psi and above, and a process in which both air and water are utilized either in combination at high pressures to propel the abrasive blast media to the surface or, in combination with relatively low pressure water used as a dust control agent or to control substrate damage have been used. Water for dust control has been mixed with the air either internally in the blast nozzle or exterior of the nozzle at the targeted surface to be cleaned and such latter process, although primarily a dry blasting technique, is considered wet blasting inasmuch as media recovery and clean up is substantially different from that utilized in a purely dry blasting operation.
The blast media or abrasive particles most widely used for blasting surfaces to remove adherent material therefrom is sand. Sand is a hard abrasive which is very useful in removing adherent materials such as paint, scale and other materials from metal surfaces such as steel. While sand is a most useful abrasive for each type of blasting technique, there are disadvantages in using sand as a blast media. For one, sand, i.e., silica, is friable and upon hitting a metal surface will break into minute particles which are small enough to enter the lungs. These minute silica particles pose a substantial health hazard. Additionally, much effort is needed to remove the sand from the surrounding area after completion of blasting. Still another disadvantage is the hardness of sand itself. Thus, sand cannot readily be used as an abrasive to remove coatings from relatively soft metals such as aluminum or any other soft substrate such as plastic, plastic composite structures, concrete or wood, as such relatively soft substrates can be excessively damaged by the abrasiveness of sand. Moreover, sand cannot be used around moving parts of machinery inasmuch as the sand particles can enter bearing surfaces and the like.
An alternative to non-soluble blast media such as sand, in particular, for removing adherent coatings from relatively soft substrates such as softer metals as aluminum, composite surfaces, plastics, concrete and the like is sodium bicarbonate. While sodium bicarbonate is softer than sand, it is sufficiently hard to remove coatings from aluminum surfaces and as well remove other coatings including paint, dirt, and grease from non-metallic surfaces without harming the substrate surface. Sodium bicarbonate is not harmful to the environment and is most advantageously water soluble such that the particles which remain subsequent to blasting can be simply washed away without yielding environmental harm.
A typical dry or wet blasting apparatus comprises a storage tank or pot to store and dispense an abrasive particulate media such as sand or bicarbonate into a highly pressurized fluid stream, a flexible hose to carry the fluid/blast media mixture to the blast nozzle and which allows the operator to move the blast nozzle relative to the surface to be cleaned and a blast nozzle which accelerates the abrasive blast media and directs same into contact with the surface to be treated. The blast nozzle is secured to the blast hose by means of a nozzle holder and is typically hand-held by the operator and moved relative to the targeted surface so as to direct the abrasive blast media across the entire surface to be treated.
The nozzle holder is used to attach the blast nozzle to the end of the blast hose allowing the nozzle to be quickly and easily changed to fit processing requirements which also may change during the course of the cleaning operation. Typically, the nozzle holder is "slip-fit" over the blast hose and is securely attached thereto via glue and screws which are threaded into the blast hose. Unfortunately, a common problem with this means to attach the blast hose to the blast nozzle is nozzle holder failure resulting in the nozzle holder separating from the blast hose during the blast cleaning operation. Most failures are caused by blast hoses having undersized outside diameters which reduce the snugness of the slip fit with the nozzle holder or by delamination of the blast hose especially around the areas in which the attachment screws have been threaded into the blast hose. The blast hoses are formed by multiple plies of rubber, the number of such plies depending upon the media which is being used. For example, if sand is the abrasive media, a rubber hose made of at least four plies and approximately 1/2 inch thick is typically used so as to resist the abrasive nature of the sand. Such a hose is relatively stiff and it is difficult for the operator to readily manipulate the hand held blast nozzle. On the other hand, if a less dense blast media such as sodium bicarbonate is used, the supply hose does not need to be as thick as for use with sand and, typically, a two-ply blast hose having a thickness about 1/4 inch has been found useful. Such hose is vastly more flexible than the supply hose used for sand and is readily manipulated by the operator. Each of the above-described supply hoses pose unique problems with respect to the attachment thereof in a nozzle holder. With a blast hose used to carry sand to the blast nozzle, the outside diameter of such hose can be uneven as it is common that as the multiple plies are wrapped upon each other differences in applied tension to the plies during the wrapping process causes the outer diameter of the supply hose to vary along the length of the hose. With respect to the more flexible hoses which comprise fewer rubber plies, the attachment screws which are used to secure the hose to the nozzle holder penetrate well into the thickness of the hose and after some time in use, the interior surface of the hose is worn down so as to expose the screws to the blast stream. Blast hose delamination initially occurs as the inside surface of the blast hose is subjected to the constant wear of the abrasive passing therethrough to the extent that the securing screws penetrate into the blast stream. The particulate blast media further weakens the hose around the penetration points resulting in the consequent delamination of the hose.
Accordingly, there is a need to provide a blast nozzle holder which can securely attach the blast hose to the blast nozzle and avoid separation of the blast hose during the blast cleaning operation.
Another need is to provide a blast nozzle holder which can securely attach the blast hose to the blast nozzle in such a manner so as to not adversely effect the integrity of the blast hose. Thus, it would be worthwhile to provide a nozzle holder which can securely attach the blast hose to the blast nozzle without utilizing attachment screws which must be threaded into the blast hose.
The objectives of the present invention are such to meet the above described needs and provide a nozzle holder which can securely attach the blast hose to the blast nozzle without adversely affecting the integrity of the blast hose.
Another objective of the present invention is to provide a blast cleaning process utilizing sodium bicarbonate as the blast media wherein the supply hose which carries the sodium bicarbonate to the blast nozzle is secured thereto by a nozzle holder without adversely altering the integrity of the supply hose.